The conventional thermometer applying on present market are mercury glass thermometer, electronic thermometer and infrared ear thermometer, conventional mercury glass thermometer has a risk of breaking in using, and the leakage of mercury may occurred and cause injury to the user, furthermore, the scale on the body of the thermometer is not easy to read, thus, electronic thermometer and infrared ear thermometer are developed, with solid plastic shell and digital display which is not only strong enough to overcome normal bump and hit in daily use, but the value is also easy to read, however, conventional electronic thermometer needs 3 to 5 minutes since start sensing to the number is shown on the screen, infrared ear thermometer needs less time, but the cost of production is expensive, besides, infrared sensor is easy to be interfered by air temperature, the material covers on the object, and the position of body for measuring, thus, the user of conventional infrared ear thermometer needs time to be familiar with the way of operation, and sometimes the inaccuracy or errors may be caused by the miss of personal operating, therefore, to provide a thermometer with shorter reactive time and more easy to use, have become a main issue of present invention.